Separation of iron by chlorination of a ferro-alloy

ABSTRACT

D R A W I N G IRON IS SEPARATED BY HALOGENATION FROM A MATERIAL, E.G. AN ALLOY, CONTAINING AT LEAST ONE OTHER METAL SELECTED FROM THE GROUP CONSISTING OF ZR, TI, HF, V, NB, TA, MO, W, AND RE WHEREIN THE MATERIAL IS CHLORINATED TO FORM A GASEOUS MIXTURE CONTAINING FERROUS CHLORIDE AND AT LEAST ONE OTHER METAL CHLORIDE, FOLLOWING WHICH THE ONE OTHER METAL CHLORIDE IS SEPARATED FROM THE FERROUS CHLORIDE BY CONDENSING OUT THE LATTER AT A TEMPERATURE AT WHICH THE AT LEAST ONE OTHER METAL CHLORIDE IS VOLATILE.

P? 24, 1973 E. K. A. SVANSTROM 3,729,544

SEPARATION OF IRON BY CHLORINATION OF A FERRO-ALLOY 2 Sheets-Sheet 1FIG.I

Original Filed June 18, 1970 FIG. 2

April 1973 E. K. A. SVANSTROM 3,

SEPARATION OF IRON BY CHLORINATION OF A FERRO-ALLOY Original Filed June18, 1970 2 Sheets-Sheet 2 Chlorino'ring Agent Condenser 23 VolofileChlorides Reactor Reactor FeClz United States Patent US. Cl. 423149 7Claims ABSTRACT OF THE DISCLOSURE Iron is separated by halogenation froma material, e.g. an alloy, containing at least one other metal selectedfrom the group consisting of Zr, Ti, Hf, V, Nb, Ta, Mo, W, and Rewherein the material is chlorinated to form a gaseous mixture containingferrous chloride and at least one other metal chloride, following whichthe one other metal chloride is separated from the ferrous chloride bycondensing out the latter at a temperature at which the at least oneother metal chloride is volatile.

This application is a continuation of US. application Ser. No. 47,366,filed June 18, 1970, now abandoned.

This invention relates to a method of separating by halogenation ironfrom materials, e.g. alloys, containing at least one other metalselected from the group consisting of the refractory metals Zr, Ti, Hf,V, Nb, Ta, M0, W, and Re.

It is known to produce halides of metals selected from the Groups 412,5b, 6b and 7b of the Periodic System of the elements (i.e. therefractory metals Zr, Ti, Hf, V, Nb, Ta, Mo, W and Re) by reacting themetal with a halogenating agent, e.g. chlorine or other gaseoushalogens. Chlorine is the most commercially interesting of thehalogenating agents. Thus, while the invention will be described fromthe viewpoint of using chlorine as the agent, it will be understood thatother halogenating agents can be used in the same manner and, forpurposes of this invention, the other halogenating agents shall bedeemed to be equivalent to chlorine.

According to the prior art, it is possible to treat ores, oxides,sulfides, etc. of the foregoing metals with chlorine at elevatedtemperatures. Generally, a reducing agent is necessary for thechlorination reaction to take place. However, such kinds of technicalstarting materials often contain substantial quantities of othercomponents that cannot be chlorinated. Such materials have theirdisadvantages in that the residues remaining after the chlorination iscompleted must be removed from the apparatus during operation whichpresents practical problems; for example, it is difiicult to extract thedesired metal component with acceptable yields.

Different methods for increasing the yields have been described inliterature. However, at present there is no satisfactory solution tothis problem. Because several of the foregoing metals are very expensive(e.g. tungsten), high yields are very necessary if the method is to bepractical. Where such expensive metals as Nb, Ta, W, Mo and V are to berecovered, it is preferred to start with metallic raw materials, such asalloys, the impure metals and carbides. The somewhat higher price forthese starting materials is not too important in view of the recoveriesachieved with the process.

The advantage of starting with metallic materials is that they can beeasily chlorinated, the amount of chlorination residues beinginsignificant and of no practical importance. By starting with metallicmaterials, the re- 3,729,544 Patented Apr. 24, 1973 covery of metal isalmost percent. The chlorination operation is fairly simple and quiteeconomical. However, a technical difiiculty connected with chlorinationof metal alloys is the problem of separating the chlorination productsformed.

This is particularly the case with ferrous alloys of, for instance, W,Nb, Ta, which are well established products in the marketplace. Themetallurgical production of these alloys is quite economical and hasbeen used for quite some time. In spite of the availability of thesealloys, they have not been used as starting materials due to thedifficulties of separating the ferric chloride formed duringchlorination from the final product. lHeated beds of sodium chloride areused, through which metal chloride vapors are passed, whereby the ferricchloride combines with the sodium chloride and is retained on the bedthis way while chlorides of, for instance, W, Nb and Ta pass through.The combination of sodium chloride and ferric chloride is drained off atthe bottom of the bed while fresh sodium chloride is added to the top ofthe bed. The use of the bed is inconvenient in that plugging occurs andalso the efficiency is poor due to excessive amounts of liquid saltremaining in the bed. In US. Pat. No. 3,407,031, a method for separatingiron chloride is disclosed wherein chlorination in a salt melt isemployed. However, this method has its disadvantages, owing tounacceptably low yields which makes the method unsuitable forcommercial.

use.

In US. Pat. No. 3,261,664, the separation of FeClfrom a mixture of TiClFeCl and FeCl is disclosed. According to the conditions describedtherein, a balance occurs such that FeCl is formed only in very smallquantities, due mainly to the formation of the dimer, Fegcla.

As far as is known, a satisfactory method has not been proposed forefficiently recovering metal halides from ion-containing metallicmaterials.

*It is thus the object of the invention to provide an economical methodfor recovering refractory metals from iron-containing materials, e.g.ferro alloys, by halogenation wherein the iron is efficiently separatedfrom the other metals.

The foregoing and other objects will more clearly appear from thefollowing disclosure and the accompanying drawing, wherein:

FIGS. 1 to 3 are schematics of apparatus embodiments which may beemployed in carrying out the invention.

Stating it broadly, a method is. provided for separating iron byhalogenation from material containing at least one other refractorymetal selected from the group consisting of Zr, Ti, Hf, V, Ta, Mo, W andRe comprising, forming a particulate bed of said material of suitabledepth in a reactor, subjecting the bed to chlorination by passing achlorinating agent through the bed from one end of the bed to the otherat a chlorinating temperature sutficient to form gaseous chloridescontaining ferrous chloride, passing the gaseous chloride through acondensing zone maintained at a temperature at which the ferrouschloride condenses while the remaining at least one metal chloride isvolatile, and then separating the at least one volatile chloride fromthe condensed ferrous chloride.

According to the invention, the chlorination is carried out such thatthe iron in the material is converted into ferrous chloride and theformation of ferric chloride avoided. In using other halogenating agentsin place of chlorine, the process is similarly carried out to formferrous halide.

Generally speaking, chlorination reactions of this type are carried outin a fixed bed by adding chlorine gas at an elevated temperature. Thechlorination gas is added under such conditions that the chlorine reactscompletely with the charge before leaving the bed. This can be effectedby means of a suitable control of the bed temperature, feed velocity ofchlorination gas, and grain size of the charge, etc. The temperature ofthe chlorination should exceed about 670 C., for example, 1000 C. Bycontrolling the reaction in this manner, the ferric chloride initiallyformed in the first reaction, as the gas enters the bed will, before itleaves the bed, reacts with the remaining charge to form ferrouschloride.

However, it is not necessary that the conversion into ferrous chloridetake place in the same bed. It may be advantageous, for example, for theconversion to be effected in a separate step, where the gaseouschlorides are reacted again with the same material and where thereaction conditions, i.e. with respect to particle size and reactiontemperature, can be the same or can be different. The gases from thefirst reactor can alternatively be reacted with any suitable materialwith good affinity for chlorine, for instance, silicon or certainferrous alloys.

In the chlorination of ferro-tungsten, an added circumstance contributesto the formation of iron chloride in bivalent form. Normally thechlorination is carried out at a temperature exceeding 670 C. Tungstenis then converted to WCl which is the thermodynamically stable chlorideat higher temperatures. If the chlorination conditions are favorable,the iron is simultaneously converted to FeCl A less complete conversionof the chlorine in the reaction zone results, to start with, in theformation of FeCl and, when essentially all iron is obtained as FeClfree C1 will occur in the chlorination products if the chlorination rateis still lower.

[When the temperature of the gaseous chlorination products is lowered tomake possible the separation of FeCl in solid form, WCl will take onechlorine from Fe Cl to form WCl and FeCl according to the equation:

A requirement for the reaction to proceed to the right to an essentialdegree is that the temperature does not exceed about 400 C., whichtemperature is also suitable from the standpoint of separating out theferrous chloride.

As ferrous chloride has a very high boiling point compared with ferricchloride and the refractory metal chlorides produced in the pure stateherein, ferrous chloride can be completely separated at temperaturesover the boiling point of the chlorides to be produced, such as tungstenchloride, niobium chloride, tantalum chloride, etc. This means that thetemperature of the gas mixture can be maintained at the range of about350-400 C. in the separation step. The ferrous chloride Will thenseparate in solid form from the gas mixture. On account of the very lowvapor pressure of the ferrous chloride at the temperatures used, itsseparation will be practically 100 percent. The separation is preferablycarried out in a separate vessel (e.g. a condenser), where the ferrouschloride can be deposited out. In order to insure that the fine granularferrous chloride condensed is not transported further, the gas ispreferably filtered before the other chlorides are condensed out. Aswill be appreciated, this method gives a simple and very effectivemethod for the separation of iron.

In carrying out the invention, the apparatus of either FIGS. 1 or 2 maybe employed, among others. Referring to FIG. 1, a hopper 1 is shown fromwhich the raw material to be chlorinated is charged into reactor 4 viavalve or gate 3. A chlorinating gas, e.g. C1 is fed via tube 2 intoreactor 4 containing a particulate charge 4A of a ferro-tungsten alloy.The reactor comprises a ceramic lining 5 which converges to a smallercross section at 5A to leave a reduced opening at 11 at which a bridgingelement 12 is provided across it to insure support of bed 4A whileallowing chlorinating gas to pass through the charge from the topthrough the bottom thereof and through opening 11. The reaction beingexothermic is carried out at above 670 C., e.g. at about 1000 C. or 1050C.

The reactor communicates with a large condensing chamber 13 which ismaintained at a lower temperature, eg. 350 C. to 400 C. via electricheating elements 6 embedded in insulation 7 surrounding the outersurface of the chamber. The ferrous chloride condenses to a solid 8 atthe bottom of the chamber as shown and at regular intervals is removedfrom it by opening closure element 14. Coupled to the condensing chamberis an enclosed filter 9 and an exit port 10 through which the volatilemetal chlorides to be recovered are withdrawn for subsequent separationby condensation. The filter 9 separates finely suspended solid ferrouschloride particles from the volatile metal chlorides. As will be notedfrom FIG. 1, the gaseous chlorinating agent passes from the top of thecharge through the bottom thereof.

FIG. 2 is similar to FIG. 1 and similar elements are identified by thesame numerals, except that the chlorinating agent enters through tube 2in the bottom of the charge and out through the top thereof. Theparticulate charge 4A is fed via hopper 1 by way of valve or gate 3 withreactor 4 similarly insulated by ceramic 5, a bridging element 12 beingprovided at the reduced end or bottom of the reactor for assuringsupport of the charge bed. As the chlorinating agent passes through thecharge from the bottom thereof, the volatile chlorides formed are ledoff through conduit 15 into condensing chamber similarly maintained at alower temperature (e.g. 350 C. to 400 C.) by means of heating elements 6embedded in insulation 7. Solids of ferrous chloride 8 are condensed outin chamber 13 as shown in FIG. 2, the solids being removed at regularintervals by opening closure element 14. As in FIG. 1, a filter 9 andexit port 10 is coupled to the coudenser through which the volatilechlorides are removed after filtering out any suspended solids offerrous chloride.

As stated hereinbefore, as the chlorinating agent enters the charge,whether through the top or the bottom thereof, ferric chloride is firstformed which is reduced to ferrous chloride as it passes through theremainder of the charge. An alternative approach is to have two beds intandem series connected so that the volatile chlorides formed in thefirst bed are comprised of ferric chloride in addition to the othermetal chlorides which chlorides are then passed through the second bedcontaining the same charge or other material for reducing the ferricchloride. The beds may both be at about 1000 C.

A schematic flow sheet of the foregoing is shown in FIG. 3 comprisingfirst and second reactors 20 and 21, respectively, series connected sothat the chlorinating agent 22 (e.g. chlorine) passing through the firstbed of, for example, ferro-tungsten, from the top through the bottomthereof results in volatile chloride gases containing ferric chlorideand tungsten chloride. The volatile gases are then fed through thesecond bed (reactor 21) where the ferric chloride is reduced to ferrouschloride which is thereafter condensed out in condenser 23, the volatiletungsten chloride being thereafter removed at 24.

As illustrative of the invention, the following examples are given:

EXAMPLE 1 A ferro-tungsten alloy having the composition of 70% W, 25% Feand 4% Si and some incidentals was chlorinated in a heat insulatedquartz tube. The reaction was started by heating the lower part of thecharge to about 500 C., Whereafter chlorine was added. The weight of thecharge at the start of the chlorination with 4.4 kgs. During the courseof the chlorination, a further addition of 6.0 kgs. of alloy was made.At the end of the test, 4.9 kgs. of unreacted material remained in thebed. Chlorine was added at a rate of 60 g./min. The temperature in thereaction zone during the chlorination was about 1050" C. The volatilereaction products were transported from the reactor into a containerwhich was kept at a temperature of about 400 C. and where the ferrouschloride was separated by condensation in the solid state from thegaseous tungsten chloride. The uncondensed chlorides were passed furtherthrough a filter and through a heated tube to a condenser where thetungsten chloride was separated. About 8.2 kgs. of tungsten chloride and3.2 kgs. of ferrous chloride were collected in the respective receivingcontainers. Analysis of the tungsten chloride showed a content of 50 mg.iron per kg. of tungsten or a very low iron content of only 0.005%.

EXAMPLE 2 Niobium and tantalum are recovered from a ferroniobium alloycontaining about 68% niobium, 7% tantalum and 25% iron by forming afirst and second particulate bed of the alloy using the flow sheet ofFIG. 3. About 10 kgs. of the alloy are placed in each of the reactors 20and 21. The first reactor is maintained at a temperature of about 800C., the second one at about 1000 C. Chlorine is passed through reactor20 at a rate of 50 g./min. to provide volatile chlorides containingferric chloride, niobium chloride and tantalum chloride, the volatilechlorides being then passed through the second bed where the ferricchloride is reduced to ferrous chloride, following which the ferrouschloride is removed from the niobium and tantalum chlorides bycondensation in a condenser 23 maintained at a temperature ofapproximately 400 C.

EXAMPLE 3 Perm-molybdenum containing about 73% molybdenum, 25 iron and2% Si is treated similarly as in Example l. The reaction is carried outwith about 8 kgs. of the particulate alloy at a temperature of about 950C., the chlorine being fed at a rate of about 60 grams per minute toprovide a volatile chloride mixture of ferrous chloride and molybdenumchloride. The ferrous chloride is condensed out as described in Example1 and the mlybdenum chloride thereafter separated out from the condensedferrous chloride.

EXAMPLE 4 Ferro-titanium comprising about 65% titanium and 35% iron istreated similarly as in Example 1. The reaction is carried out withabout 5 kgs. of particulate alloy at a temperature of about 975 C., thechlorine being fed at a rate of about 75 grams per minute to provide avolatile chloride mixture of ferrous chloride and titaniumtetrachloride. The ferrous chloride is condensed out as described inExample 1 at a temperature of about 400 C. and the titaniumtetrachloride then recovered as a gas.

As is apparent from the foregoing, by converting the iron in the alloyto ferrous chloride, it makes it relatively easy to separate the ironfrom the other volatile chlorides. This will be apparent by comparingthe properties of FeCl with certain of refractory metal chlorides asfollows (Handbook of Chemistry and Physics, 28th edition, 1944):

Metal chloride Sublimes.

Examples of materials (e.g. alloys) which may be treated in accordancewith the invention are the fol lowing:

5 Material: Typical analysis (1) Ferro-tungsten 83% W, 16% Fe, 1% C. (2)Iron-silicon tungsten alloy. 80% W, Fe, 10% Si. (3) Ferro-niobium 68%Nb, 7% Ta, 25% Fe. (4) Ferro-vanadium 56% V, 41% Fe, 3% Si. (5)Ferro-molyb- 71% Mo, 28% Fe, 1% 'Si.

den-um.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariatio s may be resorted to without departing from the spirit" andscope of the invention as those skilled in the art will readily 2Ounderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and the appended claims.

\Vhat is claimed is:

1. A method of separating iron by halogenation from a ferro-tungstenalloy which comprises:

forming a particulate bed of said alloy of suitable depth in a reactor,

subjecting said bed to chlorination by passing gaseous chlorine in theabsence of a reducing agent from one end of the bed through said depthto the other end thereof at a temperature of at least about 670 C. toform gaseous chlorides such that any ferric chloride formed initially asthe gas enters the bed reacts with the remainder of the bed to formferrous chloride,

passing said gaseous chlorides containing tungsten chloride and saidferrous chloride essentially free of any ferric chloride through acooling zone maintained at a temperature at which said ferrous chloridecondenses in solid form whi.e at least the tungsten chloride isvolatile,

and then separating the tungsten chloride from the solid ferrous-chloride.

2. The method of claim 1, wherein the temperature of the condensing zoneis about 350 C. to 400 C.

3. A method of separating iron by halogenation of a ferro-alloycontaining a substantial proportion of at least one metal selected fromthe group consisting of Zr, Ti, Hf, V, Nb, Ta, Mo, W and Re, whichcomprises:

treating a first particulate bed of said ferro-alloy with gaseouschlorine in the absence of a reducing agent to provide a gaseouschloride mixture containing ferric chloride and at least one of saidother metal chlorides,

passing the gaseous chloride mixture containing the ferric chloridethrough a second particulate bed formed of a material selected from thegroup consisting of ferro-alloys and silicon, whereby to reduce saidferric chloride to ferrous chloride in the mixture,

passing the thus formed gaseous chloride mixture through a cooling zonemaintained at a temperature at which the ferrous chloride condenses insolid form while the remaining at least one metal chloride is volatile,

and then separating the at least one volatile metal chloride from thesolid ferrous chloride.

4. The method of claim 3, wherein the material in the second particulatebed is substantially the material of the first particulate bed.

5. The method of claim 3, wherein the material of the second particulatebed comprises silicon.

6. The method of claim 3, wherein the material chlorinated is aferro-tungsten alloy which is chlorinated at a temperature exceeding 670C., and wherein tungsten chloride formed by reaction is subsequentlyseparated from the condensed ferrous chloride.

7. The method of claim 6, wherein the temperature of the condensing zoneis about 350 C. to 400 C.

References Cited UNITED 8 Mayer 423-67 Sutherland 423-62 Cairns et a1.423-149 X Peterson et a1. 423-491 UX OTHER REFERENCES Extraction andRefining of the 'Rarer Metals, 21 Symposium book, 1957, pp. 274 and 287.The Institution of Mining and Metallurgy, London.

